This invention relates generally to the field of integrated circuits, and more particularly, to a reduced surface field (RESURF) device having an extended field plate and method for forming the same.
A reduced surface field (RESURF) semiconductor device comprises a shallow n-type region doped or implanted into an epitaxial layer. In such RESURF devices, high breakdown voltage (Bvdss) can be achieved during OFF-state operation. Accordingly, these devices are attractive for various applications, such as building cost effective, intelligent power designs, as they are smaller than other devices used for power applications and can therefore reduce the area needed for a power device. Previously, in order to provide a higher breakdown voltage in a RESURF device, the doping of the RESURF implant was decreased. However, this technique also introduced numerous undesirable electrical properties into the semiconductor device, such as, for example, increasing the ON-state resistance of the device, and hence, response time. Thus, prior designs of RESURF semiconductor devices were a compromise of various desired characteristics.
Accordingly, a need has arisen for a reduced surface field semiconductor device and method of fabrication that addresses the shortcomings of the prior reduced surface field semiconductor devices and methods of fabrication.
According to an embodiment of the present invention, a semiconductor device comprises a reduced surface field (RESURF) implant. A field oxide layer, having a length, is formed over the RESURF implant. A field plate extends from a near-side of the field oxide layer and over at least one-half of the length of the field oxide layer.
According to another embodiment of the present invention, a semiconductor device comprises a reduced surface field (RESURF) implant. A field oxide layer is formed over the RESURF implant as a LOCOS structure having a near-side bird""s beak and a far-side bird""s beak. The field oxide layer has a length defined as the distance between the near-side bird""s beak and the far-side bird""s beak. A field plate extends from the near-side bird""s beak and over at least one-half of the length of the field oxide layer.
According to yet another embodiment of the present invention, a method for forming a semiconductor device comprises the following steps: forming a reduced surface field (RESURF) implant in an epitaxial layer; forming a field oxide layer over the RESURF implant, the field oxide layer having a length; and forming a field plate over at least a portion of the field oxide layer, the field plate extending from a near-side of the field oxide layer and over at least one-half of the length of the field oxide layer.
An important technical advantage of the present invention includes providing a reduced surface field (RESURF) semiconductor device having a field plate which extends over at least half the length of a field oxide layer beginning from the side of the field oxide layer adjacent or nearest to a gate of the semiconductor device. In one embodiment, the field oxide layer may be formed as a LOCOS (LOCal Oxidation of Silicon) structure having a near-side bird""s beak proximate the gate and a far-side bird""s beak proximate a drain of the semiconductor device; the field plate can be extended up to one alignment tolerance of the far-side bird""s beak of the field oxide layer. Such an extended field plate provides higher breakdown voltage in the OFF-state of the semiconductor device, while not substantially increasing resistance in the ON-state. Thus, there is no need to compromise between various desirable characteristics when designing or forming the semiconductor device. Other important technical advantages of the present invention are readily apparent to one skilled in the art from the following figures, description, and claims.